Unsettled Weather & Active Atlantic Tropics

My rough analysis of local conditions. Red dashed line indicating the rough location of a weak trough to the north of Bermuda. Red arrows indicate rough surface wind streamlines converging near Bermuda around as they meet coming around the ridge in the Bermuda-Azores high to the south of Bermuda. The Aqua arrow is a wind streamline indicating the location of the low associated with the TUTT. While the blue line with flags indicates a cold front.

The weather of the last three days has been unsettled with heavy isolated showers bringing nearly 2″ of rain in some spots. A weak cold front that approached the island from the north disintegrated on approach leaving a fragmented area of weak surface troughing that has interacted with an upper level low associated with the semi-permanent tropical upper-tropospheric trough (TUTT) to the southeast of Bermuda. This has allowed for showers and thunderstorms to develop near the island. However, because the surface trough is poorly defined – allowing only weak surface convergence – showers should remain intermittent and isolated until this feature moves away to the north. Surface outflow boundaries from collapsing showers and thunderstorms may occasionally result in sudden wind shifts and allow for locally enhanced convergence that could lead to additional shower development in a similar fashion to small scale cold fronts.

The upper level low to the southeast is enhancing shower and thunderstorm activity near its center as it weakens and drifts to the west, remaining south of Bermuda. This feature should be monitored for surface development that could lead to sub-tropical or tropical development. The chances of this are very low and aren’t supported by model data, but the proximity to Bermuda, the area of surface convergence nearby, and the fact that it is over some of the warmest waters of the Atlantic means it warrants a close eye. Regardless, expect the weak system creating showers to clear away to the north by Friday night, leaving more settled weather for the weekend as the Bermuda-Azores high extends a ridge back across Bermuda. Shower activity will continue as typical summer warmth combined with convergence ahead of a front stalling to the north of Bermuda produce isolated showers on generally southerly surface winds that back more southeasterly to easterly as the ridge shifts to the north of the island through the weekend. See the Bermuda Weather Service for the latest official forecasts, watches, warnings, and observations.

My estimated location of the tropical wave in the Western Caribbean as a red dashed line. GOES Floater unenhanced infrared satellite imagery.

Otherwise, two tropical disturbances are being monitored by the National Hurricane Center. The first, a tropical wave in the Western Caribbean, has evolved from a African Easterly wave that crossed the Atlantic – suppressed by dry Saharan air. As of the 9pm Bermuda time update, it is given a high, 70% chance for becoming a tropical cyclone in the next 48hours. It is expected to track west and northwest into and across the Yucatan peninsula to emerge in the Gulf of Mexico. Hurricane hunter aircraft are scheduled to investigate this disturbance tomorrow. However, this disturbance is not an immediate threat to Bermuda. While, it was initially hindered by dry air, this tropical wave has moved into a very wet environment and has a lot of persistent convective activity, but no closed surface circulation and so cannot be called a tropical cyclone.

My estimated location of the center of a tropical low near the Cape Verde Islands as a red ‘L’. GOES Floater unenhanced infrared satellite imagery.

The other disturbance, near the Cape Verde islands, rolled off the African coast as a tropical low rather than wave. Satellite derived winds suggest that it has a closed circulation and is close to becoming a tropical cyclone. However, it is lacking in convective organization – that is, the showers and thunderstorms have not become persistent in the fashion that characterizes a tropical cyclone. The National Hurricane Center gives this tropical low a high 80% chance of becoming a tropical cyclone in the next 48hours in their 9pm Bermuda time update.

China Meteorological Agency radar image out of Yangjiang, Guangzhou, China at 04z August 14th 2013. This image captures the eye of Typhoon Utor just offshore before making a landfall near the radar site.

In the Western Pacific, Typhoon Utor rapidly intensified to Super Typhoon strength, but a last minute eye-wall replacement cycle weakened the storm before it made landfall in Luzon in the Philippines as a category 4 equivalent typhoon with 130mph 1-minute sustained winds (JTWC). Fortunately, the strongest winds were confined to a small area and quickly weakened as Utor moved inland into Luzon. Utor crossed into the South China Sea where it emerged as a much weaker typhoon. Utor then slowly restrengthened to category three equivalent intensity before moving northwest for a landfall in southern China near Yangjiang City – to the west of Hong Kong. Again, it weakened to a category two equivalent storm with 100mph 1-minute sustained winds (JTWC). This typhoon delivered damaging typhoon strength winds to both landfall locations along with heavy flooding rains. For the latest forecast tracks and intensities on West Pacific Typhoons, see the Japanese Meteorological Agency (JMA), the Joint Typhoon Warning Center (JTWC), the China Meteorological Agency, or the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA).